|Publication number||US7033708 B2|
|Application number||US 10/442,432|
|Publication date||Apr 25, 2006|
|Filing date||May 20, 2003|
|Priority date||May 20, 2003|
|Also published as||US20040234869|
|Publication number||10442432, 442432, US 7033708 B2, US 7033708B2, US-B2-7033708, US7033708 B2, US7033708B2|
|Original Assignee||Intel Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Non-Patent Citations (1), Referenced by (4), Classifications (14), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Reliably determining the level of defocus in a printed pattern is an important aspect of photolithography. A common focus monitoring scheme employs a 90° phase shifting transition on a mask. Such a 90° phase transition may be produced by etching a region on a glass mask by a depth that produces a relative phase difference of 90° for light transmitted through the etched and un-etched mask regions. The image intensity may be reduced at the 90° phase edge relative to the clear glass regions of the mask. The location of the intensity minimum near the phase edge is known to shift from one side of its nominal position to another as the image focus is changed from negative to positive defocus. A focus monitor may track the image plane location of a printed line that straddles a 90° phase step on a mask.
In order to effectively transfer the mask pattern to the wafer, the image must be adequately focused on the surface to be exposed. Focus is typically quantified as an offset error in the location of the wafer (or, more particularly, the surface to be exposed) in the Z-axis dimension relative to a perfectly focused image plane. This focus offset (or “defocus”) may have a positive or negative Z-axis displacement with respect to the ideal focal plane, along with a magnitude representative of the distance by which the surface is offset from the ideal focal plane (measured, for example, in micrometers). Accurate adjustment of the wafer for proper focus may be achieved by determining the direction of defocus (i.e., the positive or negative Z-axis translation of the wafer), along with an actual offset displacement measurement.
A common focus monitoring scheme employs a 90° phase shifting transition on a mask. Such a 90° phase transition may be produced by etching a region on a glass mask by a depth that produces a relative phase difference of 90° for light transmitted through the etched and unetched mask regions. The image intensity may be reduced at the 90° phase edge relative to the clear glass regions of the mask. The location of the intensity minimum near the phase edge is known to shift from one side of its nominal position to another as the image focus is changed from negative to positive defocus. A focus monitor may track the image plane location of a printed line that straddles a 90° phase step on a mask.
The mask 110 may be an alternating phase shift mask (alt-PSM), which includes a 90° phase shifting region for focus monitoring. The 90° phase shifting region may be in a frame region, e.g., over a wafer scribe line, so as not to interfere with the integrated circuit device regions on the wafer.
The 90° phase shifting region may include sub-wavelength structures, as shown in
The principle behind the effective phase shifting effect is that deep sub-wavelength features may not be effectively sampled by the incident electromagnetic wave, and as a result, their electromagnetic properties are effectively their spatially averaged properties. This may be represented by the expression
where φ is the approximate effective phase shift, φetch is the typical phase shift for the etch depth, and
is the ratio of the area of the etched regions in the phase shifting region to the entire area of the phase shifting region (also referred to here as the “duty cycle”). For instance, a sub-wavelength glass grating with a step height that corresponds to a 180° phase shift and a 50% duty cycle, effectively responds to the electromagnetic wave as a region with a 90° phase shift. In general, the exact phase shift produced in a region with sub-wavelength structures must be measured experimentally or calculated by numerically solving Maxwell's equations for the case of light propagating through the mask.
The duty cycle of the grating may determine the effective phase shift and may be adjusted if a different phase shift is desired. For example, a focus monitor may provide good results with an effective phase shift of 60° to 120° (ħm×180°), where m is an integer. The critical property of the sub-wavelength features is lateral size and average height corresponding to the effective phase shift. The lateral shape and configuration of the structures may not be important as long as their average height is approximately constant over a wavelength. The lateral size of the structures, including both the etched areas and the remaining unetched features, may need to be smaller than about λ/2 , where λ is the wavelength of the incident light. The performance of the phase shifting region may be significantly improved if the structures have lateral dimensions of roughly λ/3 or smaller. For 193-nm wafer exposures, the phase shift focus monitor features may need to be in the sub-100 nm regime.
By providing a focus monitor with an effective phase shift of, e.g., 60° to 120° using features having the same etch depth as the primary features in the mask, e.g., a 180° etch depth, the focus monitor may be produced on the mask using fewer processing steps and at lower cost than by producing a focus monitor by etching the features to a depth corresponding to a 60° to 120° phase shift.
As used herein, the term “light” refers to light used in photolithography. The terms “light” and “photolithography” in the specification need not be restricted to visible light, but can also embrace other forms of radiation and lithography.
Although the focus monitor has been described in relation to alt-PSMs, the focus monitor may be used with other mask structures. For example, the mask may be a reflective mask including thin film phase shifting features to shift the phase of the incident light. Such a mask may be used for, e.g., extreme ultraviolet lithography (EUVL).
A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US5300786 *||Oct 28, 1992||Apr 5, 1994||International Business Machines Corporation||Optical focus phase shift test pattern, monitoring system and process|
|US6440616 *||Sep 27, 2000||Aug 27, 2002||Kabushiki Kaisha Toshiba||Mask and method for focus monitoring|
|US20040029023 *||Apr 22, 2002||Feb 12, 2004||Akio Misaka||Photomask, productyion method of the same, pattern forming method using the photomask|
|1||*||Levinson, Harry J., Principles of Lithography, 2001, SPIE-The International Society of Optical Engineering, p. 274, formula 8.18.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US7438997 *||May 14, 2004||Oct 21, 2008||Intel Corporation||Imaging and devices in lithography|
|US7732106 *||Oct 20, 2008||Jun 8, 2010||Intel Corporation||Methods for etching devices used in lithography|
|US20050255388 *||May 14, 2004||Nov 17, 2005||Intel Corporation||Imaging and devices in lithography|
|US20090042111 *||Oct 20, 2008||Feb 12, 2009||Intel Corporation||Imaging and devices in lithography|
|U.S. Classification||430/5, 355/61, 356/401, 356/624, 216/12|
|International Classification||G03F1/30, G03F7/20, C03B23/00, G03F7/207, G01B11/14|
|Cooperative Classification||G03F7/70641, G03F1/30|
|European Classification||G03F1/30, G03F7/70L10F|
|May 20, 2003||AS||Assignment|
Owner name: INTEL CORPORATION, CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:TEJNIL, EDITA;REEL/FRAME:014105/0287
Effective date: 20030515
|Nov 30, 2009||REMI||Maintenance fee reminder mailed|
|Apr 25, 2010||LAPS||Lapse for failure to pay maintenance fees|
|Jun 15, 2010||FP||Expired due to failure to pay maintenance fee|
Effective date: 20100425